The Notch signaling regulates various biological functions centering around developmental processes. Although Notch, a transmembrane protein, is extensively expressed, the Notch signaling is not activated in all cells, because the Notch signaling is activated by a signal being transmitted from Delta present on a neighboring cell membrane.
Several experiments have been conducted to detect the activation of the Notch signaling. For example, since the activation of the Notch signaling eventually leads to transactivation of Hes-1 gene in a nucleus, by using the activation of Hes-1 promoter as an indicator of the activation of Notch signaling, luciferase was made to be expressed under the control of the HES-1 promoter according to the activation of Notch signals (Jarriault, S., Brou, C., Logeat, F., Schroeter, E. H., Kopan, R. and Israel, A. (1995) Signalling downstream of activated mammalian Notch. Nature 377, 355-8.). It is also the case for immunohistochemical staining performed using an antibody against activated Notch1, (Tokunaga A. Kohyama, J., Yoshida, and T., Nakao, K., Sawamoto, K., and Okano, H. (2004). Mapping spatio-temporal activation of Notch signaling during neurogenesis and gliogenesis in the developing mouse brain. J. Neurochem. 90, 142-154.). These approaches have made it possible to detect the activation of the Notch signaling.